Linux Fundamentals
Paul Cobbaut
Linux Fundamentals
Paul Cobbaut
lt-2.0
Published Thu 01 Aug 2013 01:00:39 CEST

Abstract
This book is meant to be used in ...
Table of Contents
I. introduction to Linux ..................................................................................
List of Tables
18.1. getting to command mode .........................................................................
18....
Part I. introduction to Linux
Chapter 1. Linux history
Table of Contents
1.1. Linux history ...............................................................
Linux history

1.1. Linux history
All modern operating systems have their roots in 1969 when Dennis Ritchie and
Ken Thomps...
Chapter 2. distributions
Table of Contents
2.1.
2.2.
2.3.
2.4.
2.5.

Red Hat ................................................
distributions

2.1. Red Hat
Red Hat is a billion dollar commercial Linux company that puts a lot of effort in
developing L...
Chapter 3. licensing
Table of Contents
3.1.
3.2.
3.3.
3.4.
3.5.
3.6.
3.7.
3.8.

about software licenses .....................
licensing

3.1. about software licenses
There are two predominant software paradigms: Free and Open Source Software
(FOSS)...
licensing

3.3. Free Software or Open Source Software
Both the Free Software (translates to vrije software in Dutch and to...
licensing
In case you use the software internally (including over a network), you may modify
the software without being ob...
Chapter 4. getting Linux at home
Table of Contents
4.1.
4.2.
4.3.
4.4.
4.5.

download a Linux CD image ......................
getting Linux at home

4.1. download a Linux CD image
Start by downloading a Linux CD image (an .ISO file) from the distri...
getting Linux at home

4.3. create a virtual machine
Now start Virtualbox. Contrary to the screenshot below, your left pan...
getting Linux at home
Name your virtual machine (and maybe select 32-bit or 64-bit).

Give the virtual machine some memory...
getting Linux at home
Select to create a new disk (remember, this will be a virtual disk).

If you get the question below,...
getting Linux at home
Choose dynamically allocated (fixed size is only useful in production or on really
old, slow hardwar...
getting Linux at home
Click create to create the virtual disk.

Click create to create the virtual machine.

16
getting Linux at home

4.4. attach the CD image
Before we start the virtual computer, let us take a look at some settings ...
getting Linux at home
Remember the .ISO file you downloaded? Connect this .ISO file to this virtual
machine by clicking on...
getting Linux at home
Verify that your download is accepted. If Virtualbox complains at this point, then
you probably did ...
getting Linux at home

4.5. install Linux
The virtual machine is now ready to start. When given a choice at boot, select i...
Part II. first steps on
the command line
Chapter 5. man pages
Table of Contents
5.1. man $command ....................................................................
man pages

5.1. man $command
Type man followed by a command (for which you want help) and start reading. Press
q to quit t...
man pages

5.6. whereis
The location of a manpage can be revealed with whereis.
paul@laika:~$ whereis -m whois
whois: /usr...
man pages

5.10. mandb
Should you be convinced that a man page exists, but you can't access it, then try
running mandb.
ro...
Chapter 6. working with directories
Table of Contents
6.1.
6.2.
6.3.
6.4.
6.5.
6.6.
6.7.
6.8.
6.9.

pwd .....................
working with directories

6.1. pwd
The you are here sign can be displayed with the pwd command (Print Working
Directory). ...
working with directories

cd Another useful shortcut with cd is to just type cd - to go to the previous directory.
paul@la...
working with directories

6.4. path completion
The tab key can help you in typing a path without errors. Typing cd /et fol...
working with directories

ls -lh
Another frequently used ls option is -h. It shows the numbers (file sizes) in a more
huma...
working with directories

6.6. mkdir
Walking around the Unix file tree is fun, but it is even more fun to create your own
...
working with directories

6.8. practice: working with directories
1. Display your current directory.
2. Change to the /etc...
working with directories

6.9. solution: working with directories
1. Display your current directory.
pwd

2. Change to the...
working with directories
cd /etc ; mkdir ~/newdir

16. Create in one command the directories ~/dir1/dir2/dir3 (dir3 is a s...
Chapter 7. working with files
Table of Contents
7.1. all files are case sensitive ...........................................
working with files

7.1. all files are case sensitive
Linux is case sensitive, this means that FILE1 is different from fil...
working with files

7.4. touch
One easy way to create a file is with touch. (We will see many other ways for creating
file...
working with files

rm -rf
By default, rm -r will not remove non-empty directories. However rm accepts several
options tha...
working with files

cp multiple files to directory
You can also use cp to copy multiple files into a directory. In this ca...
working with files

7.8. rename
The rename command can also be used but it has a more complex syntax to enable
renaming of...
working with files

7.9. practice: working with files
1. List the files in the /bin directory
2. Display the type of file ...
working with files

7.10. solution: working with files
1. List the files in the /bin directory
ls /bin

2. Display the typ...
working with files
cp -r /etc/*.conf ~/etcbackup
Only *.conf files that are directly in /etc/ are copied.

12. Use rename ...
Chapter 8. working with file contents
Table of Contents
8.1.
8.2.
8.3.
8.4.
8.5.
8.6.
8.7.
8.8.

head .......................
working with file contents

8.1. head
You can use head to display the first ten lines of a file.
paul@laika:~$ head /etc/p...
working with file contents

8.3. cat
The cat command is one of the most universal tools. All it does is copy standard
inpu...
working with file contents

custom end marker
You can choose an end marker for cat with << as is shown in this screenshot....
working with file contents

8.5. more and less
The more command is useful for displaying files that take up more than one ...
working with file contents

8.7. practice: file contents
1. Display the first 12 lines of /etc/services.
2. Display the la...
working with file contents

8.8. solution: file contents
1. Display the first 12 lines of /etc/services.
head -12 /etc/ser...
Chapter 9. the Linux file tree
Table of Contents
9.1. filesystem hierarchy standard .........................................
the Linux file tree

9.1. filesystem hierarchy standard
Many Linux distributions partially follow the Filesystem Hierarchy...
the Linux file tree

9.4. binary directories
Binaries are files that contain compiled source code (or machine code). Binar...
the Linux file tree

/lib
Binaries found in /bin and /sbin often use shared libraries located in /lib. Below is
a screensh...
the Linux file tree

9.5. configuration directories
/boot
The /boot directory contains all files needed to boot the comput...
the Linux file tree

/etc/skel/
The skeleton directory /etc/skel is copied to the home directory of a newly created
user. ...
the Linux file tree

9.6. data directories
/home
Users can store personal or project data under /home. It is common (but n...
the Linux file tree

/mnt
The /mnt directory should be empty and should only be used for temporary mount
points (according...
the Linux file tree

9.7. in memory directories
/dev
Device files in /dev appear to be ordinary files, but are not actuall...
the Linux file tree

/proc conversation with the kernel
/proc is another special directory, appearing to be ordinary files...
the Linux file tree
Most files in /proc are 0 bytes, yet they contain data--sometimes a lot of data. You
can see this by e...
the Linux file tree

/proc/interrupts
On the x86 architecture, /proc/interrupts displays the interrupts.
paul@RHELv4u4:~$ ...
the Linux file tree

/sys Linux 2.6 hot plugging
The /sys directory was created for the Linux 2.6 kernel. Since 2.6, Linux...
the Linux file tree

9.8. /usr Unix System Resources
Although /usr is pronounced like user, remember that it stands for Un...
the Linux file tree

/usr/share
The /usr/share directory contains architecture independent data. As you can see, this
is a...
the Linux file tree

9.9. /var variable data
Files that are unpredictable in size, such as log, cache and spool files, sho...
the Linux file tree

/var/spool
The /var/spool directory typically contains spool directories for mail and cron, but
also ...
the Linux file tree

9.10. practice: file system tree
1. Does the file /bin/cat exist ? What about /bin/dd and /bin/echo. ...
the Linux file tree
14. Read the man page of random and explain the difference between /dev/random
and /dev/urandom.

69
the Linux file tree

9.11. solution: file system tree
1. Does the file /bin/cat exist ? What about /bin/dd and /bin/echo. ...
the Linux file tree
/etc/hosts contains hostnames with their ip address
/etc/resolv.conf should contain the ip address of ...
Part III. shell expansion
Chapter 10. commands and arguments
Table of Contents
10.1.
10.2.
10.3.
10.4.
10.5.
10.6.
10.7.

echo ........................
commands and arguments

10.1. echo
This chapter frequently uses the echo command to demonstrate shell features. The
echo c...
commands and arguments

double quotes
You can also prevent the removal of white spaces by double quoting the spaces.
Same ...
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Linux fun book

  1. 1. Linux Fundamentals Paul Cobbaut
  2. 2. Linux Fundamentals Paul Cobbaut lt-2.0 Published Thu 01 Aug 2013 01:00:39 CEST Abstract This book is meant to be used in an instructor-led training. For self-study, the intent is to read this book next to a working Linux computer so you can immediately do every subject, practicing each command. This book is aimed at novice Linux system administrators (and might be interesting and useful for home users that want to know a bit more about their Linux system). However, this book is not meant as an introduction to Linux desktop applications like text editors, browsers, mail clients, multimedia or office applications. More information and free .pdf available at http://linux-training.be . Feel free to contact the author: • Paul Cobbaut: paul.cobbaut@gmail.com, http://www.linkedin.com/in/cobbaut Contributors to the Linux Training project are: • Serge van Ginderachter: serge@ginsys.eu, build scripts and infrastructure setup • Ywein Van den Brande: ywein@crealaw.eu, license and legal sections • Hendrik De Vloed: hendrik.devloed@ugent.be, buildheader.pl script We'd also like to thank our reviewers: • Wouter Verhelst: wo@uter.be, http://grep.be • Geert Goossens: mail.goossens.geert@gmail.com, http://www.linkedin.com/in/geertgoossens • Elie De Brauwer: elie@de-brauwer.be, http://www.de-brauwer.be • Christophe Vandeplas: christophe@vandeplas.com, http://christophe.vandeplas.com • Bert Desmet: bert@devnox.be, http://blog.bdesmet.be • Rich Yonts: richyonts@gmail.com, Copyright 2007-2013 Netsec BVBA, Paul Cobbaut Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled 'GNU Free Documentation License'.
  3. 3. Table of Contents I. introduction to Linux ........................................................................................ 1 1. Linux history ............................................................................................... 2 2. distributions ................................................................................................. 4 3. licensing ...................................................................................................... 6 4. getting Linux at home ............................................................................... 10 II. first steps on the command line .................................................................... 21 5. man pages ................................................................................................. 22 6. working with directories ........................................................................... 26 7. working with files ..................................................................................... 35 8. working with file contents ........................................................................ 44 9. the Linux file tree ..................................................................................... 51 III. shell expansion .............................................................................................. 72 10. commands and arguments ....................................................................... 73 11. control operators ..................................................................................... 83 12. variables .................................................................................................. 89 13. shell history ........................................................................................... 100 14. file globbing .......................................................................................... 106 IV. pipes and commands .................................................................................. 113 15. redirection and pipes ............................................................................. 114 16. filters ..................................................................................................... 123 17. basic Unix tools .................................................................................... 136 V. vi ..................................................................................................................... 145 18. Introduction to vi .................................................................................. 146 VI. scripting ....................................................................................................... 156 19. scripting introduction ............................................................................ 157 20. scripting loops ....................................................................................... 163 21. scripting parameters .............................................................................. 170 22. more scripting ....................................................................................... 178 VII. local user management ............................................................................. 186 23. users ...................................................................................................... 187 24. groups .................................................................................................... 207 VIII. file security ............................................................................................... 213 25. standard file permissions ...................................................................... 214 26. advanced file permissions ..................................................................... 225 27. access control lists ................................................................................ 231 28. file links ................................................................................................ 235 IX. Appendices ................................................................................................... 242 A. certifications ........................................................................................... 243 B. keyboard settings .................................................................................... 245 C. hardware ................................................................................................. 247 D. License ................................................................................................... 251 Index .................................................................................................................... 258 iii
  4. 4. List of Tables 18.1. getting to command mode ......................................................................... 18.2. switch to insert mode ................................................................................. 18.3. replace and delete ...................................................................................... 18.4. undo and repeat .......................................................................................... 18.5. cut, copy and paste a line .......................................................................... 18.6. cut, copy and paste lines ............................................................................ 18.7. start and end of line ................................................................................... 18.8. join two lines ............................................................................................. 18.9. words .......................................................................................................... 18.10. save and exit vi ........................................................................................ 18.11. searching .................................................................................................. 18.12. replace ...................................................................................................... 18.13. read files and input .................................................................................. 18.14. text buffers ............................................................................................... 18.15. multiple files ............................................................................................ 18.16. abbreviations ............................................................................................ 23.1. Debian User Environment .......................................................................... 23.2. Red Hat User Environment ........................................................................ 25.1. Unix special files ....................................................................................... 25.2. standard Unix file permissions .................................................................. 25.3. Unix file permissions position ................................................................... 25.4. Octal permissions ....................................................................................... iv 147 147 148 148 148 149 149 149 150 150 151 151 151 152 152 152 206 206 216 217 217 220
  5. 5. Part I. introduction to Linux
  6. 6. Chapter 1. Linux history Table of Contents 1.1. Linux history .................................................................................................... 3 This chapter briefly tells the history of Unix and where Linux fits in. If you are eager to start working with Linux without this blah, blah, blah over history, distributions, and licensing then jump straight to Part II - Chapter 6. Working with Directories page 26. 2
  7. 7. Linux history 1.1. Linux history All modern operating systems have their roots in 1969 when Dennis Ritchie and Ken Thompson developed the C language and the Unix operating system at AT&T Bell Labs. They shared their source code (yes, there was open source back in the Seventies) with the rest of the world, including the hippies in Berkeley California. By 1975, when AT&T started selling Unix commercially, about half of the source code was written by others. The hippies were not happy that a commercial company sold software that they had written; the resulting (legal) battle ended in there being two versions of Unix in the Seventies : the official AT&T Unix, and the free BSD Unix. In the Eighties many companies started developing their own Unix: IBM created AIX, Sun SunOS (later Solaris), HP HP-UX and about a dozen other companies did the same. The result was a mess of Unix dialects and a dozen different ways to do the same thing. And here is the first real root of Linux, when Richard Stallman aimed to end this era of Unix separation and everybody re-inventing the wheel by starting the GNU project (GNU is Not Unix). His goal was to make an operating system that was freely available to everyone, and where everyone could work together (like in the Seventies). Many of the command line tools that you use today on Linux or Solaris are GNU tools. The Nineties started with Linus Torvalds, a Swedish speaking Finnish student, buying a 386 computer and writing a brand new POSIX compliant kernel. He put the source code online, thinking it would never support anything but 386 hardware. Many people embraced the combination of this kernel with the GNU tools, and the rest, as they say, is history. Today more than 90 percent of supercomputers (including the complete top 10), more than half of all smartphones, many millions of desktop computers, around 70 percent of all web servers, a large chunk of tablet computers, and several appliances (dvdplayers, washing machines, dsl modems, routers, ...) run Linux. It is by far the most commonly used operating system in the world. Linux kernel version 3.2 was released in January 2012. Its source code grew by almost two hundred thousand lines (compared to version 3.1) thanks to contributions of over 4000 developers paid by about 200 commercial companies including Red Hat, Intel, Broadcom, Texas Instruments, IBM, Novell, Qualcomm, Samsung, Nokia, Oracle, Google and even Microsoft. http://en.wikipedia.org/wiki/Dennis_Ritchie http://en.wikipedia.org/wiki/Richard_Stallman http://en.wikipedia.org/wiki/Linus_Torvalds http://kernel.org http://lwn.net/Articles/472852/ http://www.linuxfoundation.org/ http://en.wikipedia.org/wiki/Linux http://www.levenez.com/unix/ (a huge Unix history poster) 3
  8. 8. Chapter 2. distributions Table of Contents 2.1. 2.2. 2.3. 2.4. 2.5. Red Hat ............................................................................................................ Ubuntu .............................................................................................................. Debian .............................................................................................................. Other ................................................................................................................ Which to choose ? ........................................................................................... 5 5 5 5 5 This chapter gives a short overview of current Linux distributions. A Linux distribution is a collection of (usually open source) software on top of a Linux kernel. A distribution (or short, distro) can bundle server software, system management tools, documentation and many desktop applications in a central secure software repository. A distro aims to provide a common look and feel, secure and easy software management and often a specific operational purpose. Let's take a look at some popular distributions. 4
  9. 9. distributions 2.1. Red Hat Red Hat is a billion dollar commercial Linux company that puts a lot of effort in developing Linux. They have hundreds of Linux specialists and are known for their excellent support. They give their products (Red Hat Enterprise Linux and Fedora) away for free. While Red Hat Enterprise Linux (RHEL) is well tested before release and supported for up to seven years after release, Fedora is a distro with faster updates but without support. 2.2. Ubuntu Canonical started sending out free compact discs with Ubuntu Linux in 2004 and quickly became popular for home users (many switching from Microsoft Windows). Canonical wants Ubuntu to be an easy to use graphical Linux desktop without need to ever see a command line. Of course they also want to make a profit by selling support for Ubuntu. 2.3. Debian There is no company behind Debian. Instead there are thousands of well organised developers that elect a Debian Project Leader every two years. Debian is seen as one of the most stable Linux distributions. It is also the basis of every release of Ubuntu. Debian comes in three versions: stable, testing and unstable. Every Debian release is named after a character in the movie Toy Story. 2.4. Other Distributions like CentOS, Oracle Enterprise Linux and Scientific Linux are based on Red Hat Enterprise Linux and share many of the same principles, directories and system administration techniques. Linux Mint, Edubuntu and many other *buntu named distributions are based on Ubuntu and thus share a lot with Debian. There are hundreds of other Linux distributions. 2.5. Which to choose ? When you are new to Linux in 2012, go for the latest Ubuntu or Fedora. If you only want to practice the Linux command line then install one Ubuntu server and/or one CentOS server (without graphical interface). redhat.com ubuntu.com debian.org centos.org distrowatch.com 5
  10. 10. Chapter 3. licensing Table of Contents 3.1. 3.2. 3.3. 3.4. 3.5. 3.6. 3.7. 3.8. about software licenses .................................................................................... public domain software and freeware .............................................................. Free Software or Open Source Software ......................................................... GNU General Public License .......................................................................... using GPLv3 software ..................................................................................... BSD license ..................................................................................................... other licenses ................................................................................................... combination of software licenses ..................................................................... 7 7 8 8 8 9 9 9 This chapter briefly explains the different licenses used for distributing operating systems software. Many thanks go to Ywein Van den Brande for writing most of this chapter. Ywein is an attorney at law, co-author of The International FOSS Law Book and author of Praktijkboek Informaticarecht (in Dutch). http://ifosslawbook.org http://www.crealaw.eu 6
  11. 11. licensing 3.1. about software licenses There are two predominant software paradigms: Free and Open Source Software (FOSS) and proprietary software. The criteria for differentiation between these two approaches is based on control over the software. With proprietary software, control tends to lie more with the vendor, while with Free and Open Source Software it tends to be more weighted towards the end user. But even though the paradigms differ, they use the same copyright laws to reach and enforce their goals. From a legal perspective, Free and Open Source Software can be considered as software to which users generally receive more rights via their license agreement than they would have with a proprietary software license, yet the underlying license mechanisms are the same. Legal theory states that the author of FOSS, contrary to the author of public domain software, has in no way whatsoever given up his rights on his work. FOSS supports on the rights of the author (the copyright) to impose FOSS license conditions. The FOSS license conditions need to be respected by the user in the same way as proprietary license conditions. Always check your license carefully before you use third party software. Examples of proprietary software are AIX from IBM, HP-UX from HP and Oracle Database 11g. You are not authorised to install or use this software without paying a licensing fee. You are not authorised to distribute copies and you are not authorised to modify the closed source code. 3.2. public domain software and freeware Software that is original in the sense that it is an intellectual creation of the author benefits copyright protection. Non-original software does not come into consideration for copyright protection and can, in principle, be used freely. Public domain software is considered as software to which the author has given up all rights and on which nobody is able to enforce any rights. This software can be used, reproduced or executed freely, without permission or the payment of a fee. Public domain software can in certain cases even be presented by third parties as own work, and by modifying the original work, third parties can take certain versions of the public domain software out of the public domain again. Freeware is not public domain software or FOSS. It is proprietary software that you can use without paying a license cost. However, the often strict license terms need to be respected. Examples of freeware are Adobe Reader, Skype and Command and Conquer: Tiberian Sun (this game was sold as proprietary in 1999 and is since 2011 available as freeware). 7
  12. 12. licensing 3.3. Free Software or Open Source Software Both the Free Software (translates to vrije software in Dutch and to Logiciel Libre in French) and the Open Source Software movement largely pursue similar goals and endorse similar software licenses. But historically, there has been some perception of differentiation due to different emphases. Where the Free Software movement focuses on the rights (the four freedoms) which Free Software provides to its users, the Open Source Software movement points to its Open Source Definition and the advantages of peer-to-peer software development. Recently, the term free and open source software or FOSS has arisen as a neutral alternative. A lesser-used variant is free/libre/open source software (FLOSS), which uses libre to clarify the meaning of free as in freedom rather than as in at no charge. Examples of free software are gcc, MySQL and gimp. Detailed information about the four freedoms can be found here: http://www.gnu.org/philosophy/free-sw.html The open source definition can be found at: http://www.opensource.org/docs/osd The above definition is based on the Debian Free Software Guidelines available here: http://www.debian.org/social_contract#guidelines 3.4. GNU General Public License More and more software is being released under the GNU GPL (in 2006 Java was released under the GPL). This license (v2 and v3) is the main license endorsed by the Free Software Foundation. It’s main characteristic is the copyleft principle. This means that everyone in the chain of consecutive users, in return for the right of use that is assigned, needs to distribute the improvements he makes to the software and his derivative works under the same conditions to other users, if he chooses to distribute such improvements or derivative works. In other words, software which incorporates GNU GPL software, needs to be distributed in turn as GNU GPL software (or compatible, see below). It is not possible to incorporate copyright protected parts of GNU GPL software in a proprietary licensed work. The GPL has been upheld in court. 3.5. using GPLv3 software You can use GPLv3 software almost without any conditions. If you solely run the software you even don’t have to accept the terms of the GPLv3. However, any other use - such as modifying or distributing the software - implies acceptance. 8
  13. 13. licensing In case you use the software internally (including over a network), you may modify the software without being obliged to distribute your modification. You may hire third parties to work on the software exclusively for you and under your direction and control. But if you modify the software and use it otherwise than merely internally, this will be considered as distribution. You must distribute your modifications under GPLv3 (the copyleft principle). Several more obligations apply if you distribute GPLv3 software. Check the GPLv3 license carefully. You create output with GPLv3 software: The GPLv3 does not automatically apply to the output. 3.6. BSD license There are several versions of the original Berkeley Distribution License. The most common one is the 3-clause license ("New BSD License" or "Modified BSD License"). This is a permissive free software license. The license places minimal restrictions on how the software can be redistributed. This is in contrast to copyleft licenses such as the GPLv. 3 discussed above, which have a copyleft mechanism. This difference is of less importance when you merely use the software, but kicks in when you start redistributing verbatim copies of the software or your own modified versions. 3.7. other licenses FOSS or not, there are many kind of licenses on software. You should read and understand them before using any software. 3.8. combination of software licenses When you use several sources or wishes to redistribute your software under a different license, you need to verify whether all licenses are compatible. Some FOSS licenses (such as BSD) are compatible with proprietary licenses, but most are not. If you detect a license incompatibility, you must contact the author to negotiate different license conditions or refrain from using the incompatible software. 9
  14. 14. Chapter 4. getting Linux at home Table of Contents 4.1. 4.2. 4.3. 4.4. 4.5. download a Linux CD image ......................................................................... download Virtualbox ..................................................................................... create a virtual machine ................................................................................. attach the CD image ...................................................................................... install Linux ................................................................................................... 11 11 12 17 20 This book assumes you have access to a working Linux computer. Most companies have one or more Linux servers, if you have already logged on to it, then you 're all set (skip this chapter and go to the next). Another option is to insert a Ubuntu Linux CD in a computer with (or without) Microsoft Windows and follow the installation. Ubuntu will resize (or create) partitions and setup a menu at boot time to choose Windows or Linux. If you do not have access to a Linux computer at the moment, and if you are unable or unsure about installing Linux on your computer, then this chapter proposes a third option: installing Linux in a virtual machine. Installation in a virtual machine (provided by Virtualbox) is easy and safe. Even when you make mistakes and crash everything on the virtual Linux machine, then nothing on the real computer is touched. This chapter gives easy steps and screenshots to get a working Ubuntu server in a Virtualbox virtual machine. The steps are very similar to installing Fedora or CentOS or even Debian, and if you like you can also use VMWare instead of Virtualbox. 10
  15. 15. getting Linux at home 4.1. download a Linux CD image Start by downloading a Linux CD image (an .ISO file) from the distribution of your choice from the Internet. Take care selecting the correct cpu architecture of your computer; choose i386 if unsure. Choosing the wrong cpu type (like x86_64 when you have an old Pentium) will almost immediately fail to boot the CD. 4.2. download Virtualbox Step two (when the .ISO file has finished downloading) is to download Virtualbox. If you are currently running Microsoft Windows, then download and install Virtualbox for Windows! 11
  16. 16. getting Linux at home 4.3. create a virtual machine Now start Virtualbox. Contrary to the screenshot below, your left pane should be empty. Click New to create a new virtual machine. We will walk together through the wizard. The screenshots below are taken on Mac OSX; they will be slightly different if you are running Microsoft Windows. 12
  17. 17. getting Linux at home Name your virtual machine (and maybe select 32-bit or 64-bit). Give the virtual machine some memory (512MB if you have 2GB or more, otherwise select 256MB). 13
  18. 18. getting Linux at home Select to create a new disk (remember, this will be a virtual disk). If you get the question below, choose vdi. 14
  19. 19. getting Linux at home Choose dynamically allocated (fixed size is only useful in production or on really old, slow hardware). Choose between 10GB and 16GB as the disk size. 15
  20. 20. getting Linux at home Click create to create the virtual disk. Click create to create the virtual machine. 16
  21. 21. getting Linux at home 4.4. attach the CD image Before we start the virtual computer, let us take a look at some settings (click Settings). Do not worry if your screen looks different, just find the button named storage. 17
  22. 22. getting Linux at home Remember the .ISO file you downloaded? Connect this .ISO file to this virtual machine by clicking on the CD icon next to Empty. Now click on the other CD icon and attach your ISO file to this virtual CD drive. 18
  23. 23. getting Linux at home Verify that your download is accepted. If Virtualbox complains at this point, then you probably did not finish the download of the CD (try downloading it again). It could be useful to set the network adapter to bridge instead of NAT. Bridged usually will connect your virtual computer to the Internet. 19
  24. 24. getting Linux at home 4.5. install Linux The virtual machine is now ready to start. When given a choice at boot, select install and follow the instructions on the screen. When the installation is finished, you can log on to the machine and start practising Linux! 20
  25. 25. Part II. first steps on the command line
  26. 26. Chapter 5. man pages Table of Contents 5.1. man $command .............................................................................................. 5.2. man $configfile .............................................................................................. 5.3. man $daemon ................................................................................................. 5.4. man -k (apropos) ............................................................................................ 5.5. whatis ............................................................................................................. 5.6. whereis ........................................................................................................... 5.7. man sections ................................................................................................... 5.8. man $section $file .......................................................................................... 5.9. man man ........................................................................................................ 5.10. mandb ........................................................................................................... 23 23 23 23 23 24 24 24 24 25 This chapter will explain the use of man pages (also called manual pages) on your Unix or Linux computer. You will learn the man command together with related commands like whereis, whatis and mandb. Most Unix files and commands have pretty good man pages to explain their use. Man pages also come in handy when you are using multiple flavours of Unix or several Linux distributions since options and parameters sometimes vary. 22
  27. 27. man pages 5.1. man $command Type man followed by a command (for which you want help) and start reading. Press q to quit the manpage. Some man pages contain examples (near the end). paul@laika:~$ man whois Reformatting whois(1), please wait... 5.2. man $configfile Most configuration files have their own manual. paul@laika:~$ man syslog.conf Reformatting syslog.conf(5), please wait... 5.3. man $daemon This is also true for most daemons (background programs) on your system.. paul@laika:~$ man syslogd Reformatting syslogd(8), please wait... 5.4. man -k (apropos) man -k (or apropos) shows a list of man pages containing a string. paul@laika:~$ man -k syslog lm-syslog-setup (8) - configure laptop mode to switch syslog.conf ... logger (1) - a shell command interface to the syslog(3) ... syslog-facility (8) - Setup and remove LOCALx facility for sysklogd syslog.conf (5) - syslogd(8) configuration file syslogd (8) - Linux system logging utilities. syslogd-listfiles (8) - list system logfiles 5.5. whatis To see just the description of a manual page, use whatis followed by a string. paul@u810:~$ whatis route route (8) - show / manipulate the IP routing table 23
  28. 28. man pages 5.6. whereis The location of a manpage can be revealed with whereis. paul@laika:~$ whereis -m whois whois: /usr/share/man/man1/whois.1.gz This file is directly readable by man. paul@laika:~$ man /usr/share/man/man1/whois.1.gz 5.7. man sections By now you will have noticed the numbers between the round brackets. man man will explain to you that these are section numbers. Executable programs and shell commands reside in section one. 1 2 3 4 5 6 7 8 9 Executable programs or shell commands System calls (functions provided by the kernel) Library calls (functions within program libraries) Special files (usually found in /dev) File formats and conventions eg /etc/passwd Games Miscellaneous (including macro packages and conventions), e.g. man(7) System administration commands (usually only for root) Kernel routines [Non standard] 5.8. man $section $file Therefor, when referring to the man page of the passwd command, you will see it written as passwd(1); when referring to the passwd file, you will see it written as passwd(5). The screenshot explains how to open the man page in the correct section. [paul@RHEL52 ~]$ man passwd [paul@RHEL52 ~]$ man 5 passwd # opens the first manual found # opens a page from section 5 5.9. man man If you want to know more about man, then Read The Fantastic Manual (RTFM). Unfortunately, manual pages do not have the answer to everything... paul@laika:~$ man woman No manual entry for woman 24
  29. 29. man pages 5.10. mandb Should you be convinced that a man page exists, but you can't access it, then try running mandb. root@laika:~# mandb 0 man subdirectories contained newer manual pages. 0 manual pages were added. 0 stray cats were added. 0 old database entries were purged. 25
  30. 30. Chapter 6. working with directories Table of Contents 6.1. 6.2. 6.3. 6.4. 6.5. 6.6. 6.7. 6.8. 6.9. pwd ................................................................................................................. cd .................................................................................................................... absolute and relative paths ............................................................................. path completion .............................................................................................. ls ..................................................................................................................... mkdir .............................................................................................................. rmdir ............................................................................................................... practice: working with directories ................................................................. solution: working with directories ................................................................. 27 27 28 29 29 31 31 32 33 To explore the Linux file tree, you will need some basic tools. This chapter is small overview of the most common commands to work with directories : pwd, cd, ls, mkdir, rmdir. These commands are available on any Linux (or Unix) system. This chapter also discusses absolute and relative paths and path completion in the bash shell. 26
  31. 31. working with directories 6.1. pwd The you are here sign can be displayed with the pwd command (Print Working Directory). Go ahead, try it: Open a command line interface (like gnome-terminal, konsole, xterm, or a tty) and type pwd. The tool displays your current directory. paul@laika:~$ pwd /home/paul 6.2. cd You can change your current directory with the cd command (Change Directory). paul@laika$ paul@laika$ /etc paul@laika$ paul@laika$ /bin paul@laika$ paul@laika$ /home/paul cd /etc pwd cd /bin pwd cd /home/paul/ pwd cd ~ You can pull off a trick with cd. Just typing cd without a target directory, will put you in your home directory. Typing cd ~ has the same effect. paul@laika$ paul@laika$ /etc paul@laika$ paul@laika$ /home/paul paul@laika$ paul@laika$ /home/paul cd /etc pwd cd pwd cd ~ pwd cd .. To go to the parent directory (the one just above your current directory in the directory tree), type cd .. . paul@laika$ pwd /usr/share/games paul@laika$ cd .. paul@laika$ pwd /usr/share To stay in the current directory, type cd . ;-) We will see useful use of the . character representing the current directory later. 27
  32. 32. working with directories cd Another useful shortcut with cd is to just type cd - to go to the previous directory. paul@laika$ /home/paul paul@laika$ paul@laika$ /etc paul@laika$ /home/paul paul@laika$ /etc pwd cd /etc pwd cd cd - 6.3. absolute and relative paths You should be aware of absolute and relative paths in the file tree. When you type a path starting with a slash (/), then the root of the file tree is assumed. If you don't start your path with a slash, then the current directory is the assumed starting point. The screenshot below first shows the current directory /home/paul. From within this directory, you have to type cd /home instead of cd home to go to the /home directory. paul@laika$ pwd /home/paul paul@laika$ cd home bash: cd: home: No such file or directory paul@laika$ cd /home paul@laika$ pwd /home When inside /home, you have to type cd paul instead of cd /paul to enter the subdirectory paul of the current directory /home. paul@laika$ pwd /home paul@laika$ cd /paul bash: cd: /paul: No such file or directory paul@laika$ cd paul paul@laika$ pwd /home/paul In case your current directory is the root directory /, then both cd /home and cd home will get you in the /home directory. paul@laika$ / paul@laika$ paul@laika$ /home paul@laika$ paul@laika$ paul@laika$ /home pwd cd home pwd cd / cd /home pwd This was the last screenshot with pwd statements. From now on, the current directory will often be displayed in the prompt. Later in this book we will explain how the shell variable $PS1 can be configured to show this. 28
  33. 33. working with directories 6.4. path completion The tab key can help you in typing a path without errors. Typing cd /et followed by the tab key will expand the command line to cd /etc/. When typing cd /Et followed by the tab key, nothing will happen because you typed the wrong path (upper case E). You will need fewer key strokes when using the tab key, and you will be sure your typed path is correct! 6.5. ls You can list the contents of a directory with ls. paul@pasha:~$ ls allfiles.txt dmesg.txt paul@pasha:~$ httpd.conf stuff summer.txt ls -a A frequently used option with ls is -a to show all files. Showing all files means including the hidden files. When a file name on a Unix file system starts with a dot, it is considered a hidden file and it doesn't show up in regular file listings. paul@pasha:~$ ls allfiles.txt dmesg.txt httpd.conf stuff summer.txt paul@pasha:~$ ls -a . allfiles.txt .bash_profile dmesg.txt .lesshst .. .bash_history .bashrc httpd.conf .ssh paul@pasha:~$ stuff summer.txt ls -l Many times you will be using options with ls to display the contents of the directory in different formats or to display different parts of the directory. Typing just ls gives you a list of files in the directory. Typing ls -l (that is a letter L, not the number 1) gives you a long listing. paul@pasha:~$ ls -l total 23992 -rw-r--r-- 1 paul paul 24506857 2006-03-30 22:53 allfiles.txt -rw-r--r-- 1 paul paul 14744 2006-09-27 11:45 dmesg.txt -rw-r--r-- 1 paul paul 8189 2006-03-31 14:01 httpd.conf drwxr-xr-x 2 paul paul 4096 2007-01-08 12:22 stuff -rw-r--r-- 1 paul paul 0 2006-03-30 22:45 summer.txt 29
  34. 34. working with directories ls -lh Another frequently used ls option is -h. It shows the numbers (file sizes) in a more human readable format. Also shown below is some variation in the way you can give the options to ls. We will explain the details of the output later in this book. paul@pasha:~$ ls -l -h total 24M -rw-r--r-- 1 paul paul -rw-r--r-- 1 paul paul -rw-r--r-- 1 paul paul drwxr-xr-x 2 paul paul -rw-r--r-- 1 paul paul paul@pasha:~$ ls -lh total 24M -rw-r--r-- 1 paul paul -rw-r--r-- 1 paul paul -rw-r--r-- 1 paul paul drwxr-xr-x 2 paul paul -rw-r--r-- 1 paul paul paul@pasha:~$ ls -hl total 24M -rw-r--r-- 1 paul paul -rw-r--r-- 1 paul paul -rw-r--r-- 1 paul paul drwxr-xr-x 2 paul paul -rw-r--r-- 1 paul paul paul@pasha:~$ ls -h -l total 24M -rw-r--r-- 1 paul paul -rw-r--r-- 1 paul paul -rw-r--r-- 1 paul paul drwxr-xr-x 2 paul paul -rw-r--r-- 1 paul paul 24M 15K 8.0K 4.0K 0 2006-03-30 2006-09-27 2006-03-31 2007-01-08 2006-03-30 22:53 11:45 14:01 12:22 22:45 allfiles.txt dmesg.txt httpd.conf stuff summer.txt 24M 15K 8.0K 4.0K 0 2006-03-30 2006-09-27 2006-03-31 2007-01-08 2006-03-30 22:53 11:45 14:01 12:22 22:45 allfiles.txt dmesg.txt httpd.conf stuff summer.txt 24M 15K 8.0K 4.0K 0 2006-03-30 2006-09-27 2006-03-31 2007-01-08 2006-03-30 22:53 11:45 14:01 12:22 22:45 allfiles.txt dmesg.txt httpd.conf stuff summer.txt 24M 15K 8.0K 4.0K 0 2006-03-30 2006-09-27 2006-03-31 2007-01-08 2006-03-30 22:53 11:45 14:01 12:22 22:45 allfiles.txt dmesg.txt httpd.conf stuff summer.txt 30
  35. 35. working with directories 6.6. mkdir Walking around the Unix file tree is fun, but it is even more fun to create your own directories with mkdir. You have to give at least one parameter to mkdir, the name of the new directory to be created. Think before you type a leading / . paul@laika:~$ mkdir MyDir paul@laika:~$ cd MyDir paul@laika:~/MyDir$ ls -al total 8 drwxr-xr-x 2 paul paul 4096 2007-01-10 21:13 . drwxr-xr-x 39 paul paul 4096 2007-01-10 21:13 .. paul@laika:~/MyDir$ mkdir stuff paul@laika:~/MyDir$ mkdir otherstuff paul@laika:~/MyDir$ ls -l total 8 drwxr-xr-x 2 paul paul 4096 2007-01-10 21:14 otherstuff drwxr-xr-x 2 paul paul 4096 2007-01-10 21:14 stuff paul@laika:~/MyDir$ mkdir -p When given the option -p, then mkdir will create parent directories as needed. paul@laika:~$ paul@laika:~$ MySubdir2 paul@laika:~$ ThreeDeep paul@laika:~$ mkdir -p MyDir2/MySubdir2/ThreeDeep ls MyDir2 ls MyDir2/MySubdir2 ls MyDir2/MySubdir2/ThreeDeep/ 6.7. rmdir When a directory is empty, you can use rmdir to remove the directory. paul@laika:~/MyDir$ rmdir otherstuff paul@laika:~/MyDir$ ls stuff paul@laika:~/MyDir$ cd .. paul@laika:~$ rmdir MyDir rmdir: MyDir/: Directory not empty paul@laika:~$ rmdir MyDir/stuff paul@laika:~$ rmdir MyDir rmdir -p And similar to the mkdir -p option, you can also use rmdir to recursively remove directories. paul@laika:~$ mkdir -p dir/subdir/subdir2 paul@laika:~$ rmdir -p dir/subdir/subdir2 paul@laika:~$ 31
  36. 36. working with directories 6.8. practice: working with directories 1. Display your current directory. 2. Change to the /etc directory. 3. Now change to your home directory using only three key presses. 4. Change to the /boot/grub directory using only eleven key presses. 5. Go to the parent directory of the current directory. 6. Go to the root directory. 7. List the contents of the root directory. 8. List a long listing of the root directory. 9. Stay where you are, and list the contents of /etc. 10. Stay where you are, and list the contents of /bin and /sbin. 11. Stay where you are, and list the contents of ~. 12. List all the files (including hidden files) in your home directory. 13. List the files in /boot in a human readable format. 14. Create a directory testdir in your home directory. 15. Change to the /etc directory, stay here and create a directory newdir in your home directory. 16. Create in one command the directories ~/dir1/dir2/dir3 (dir3 is a subdirectory from dir2, and dir2 is a subdirectory from dir1 ). 17. Remove the directory testdir. 18. If time permits (or if you are waiting for other students to finish this practice), use and understand pushd and popd. Use the man page of bash to find information about these commands. 32
  37. 37. working with directories 6.9. solution: working with directories 1. Display your current directory. pwd 2. Change to the /etc directory. cd /etc 3. Now change to your home directory using only three key presses. cd (and the enter key) 4. Change to the /boot/grub directory using only eleven key presses. cd /boot/grub (use the tab key) 5. Go to the parent directory of the current directory. cd .. (with space between cd and ..) 6. Go to the root directory. cd / 7. List the contents of the root directory. ls 8. List a long listing of the root directory. ls -l 9. Stay where you are, and list the contents of /etc. ls /etc 10. Stay where you are, and list the contents of /bin and /sbin. ls /bin /sbin 11. Stay where you are, and list the contents of ~. ls ~ 12. List all the files (including hidden files) in your home directory. ls -al ~ 13. List the files in /boot in a human readable format. ls -lh /boot 14. Create a directory testdir in your home directory. mkdir ~/testdir 15. Change to the /etc directory, stay here and create a directory newdir in your home directory. 33
  38. 38. working with directories cd /etc ; mkdir ~/newdir 16. Create in one command the directories ~/dir1/dir2/dir3 (dir3 is a subdirectory from dir2, and dir2 is a subdirectory from dir1 ). mkdir -p ~/dir1/dir2/dir3 17. Remove the directory testdir. rmdir testdir 18. If time permits (or if you are waiting for other students to finish this practice), use and understand pushd and popd. Use the man page of bash to find information about these commands. man bash The Bash shell has two built-in commands called pushd and popd. Both commands work with a common stack of previous directories. Pushd adds a directory to the stack and changes to a new current directory, popd removes a directory from the stack and sets the current directory. paul@laika:/etc$ cd /bin paul@laika:/bin$ pushd /lib /lib /bin paul@laika:/lib$ pushd /proc /proc /lib /bin paul@laika:/proc$ paul@laika:/proc$ popd /lib /bin paul@laika:/lib$ paul@laika:/lib$ paul@laika:/lib$ popd /bin paul@laika:/bin$ 34
  39. 39. Chapter 7. working with files Table of Contents 7.1. all files are case sensitive .............................................................................. 7.2. everything is a file ......................................................................................... 7.3. file .................................................................................................................. 7.4. touch ............................................................................................................... 7.5. rm ................................................................................................................... 7.6. cp .................................................................................................................... 7.7. mv .................................................................................................................. 7.8. rename ............................................................................................................ 7.9. practice: working with files ........................................................................... 7.10. solution: working with files ......................................................................... 36 36 36 37 37 38 39 40 41 42 In this chapter we learn how to recognise, create, remove, copy and move files using commands like file, touch, rm, cp, mv and rename. 35
  40. 40. working with files 7.1. all files are case sensitive Linux is case sensitive, this means that FILE1 is different from file1, and /etc/hosts is different from /etc/Hosts (the latter one does not exist on a typical Linux computer). This screenshot shows the difference between two files, one with upper case W, the other with lower case w. paul@laika:~/Linux$ ls winter.txt Winter.txt paul@laika:~/Linux$ cat winter.txt It is cold. paul@laika:~/Linux$ cat Winter.txt It is very cold! 7.2. everything is a file A directory is a special kind of file, but it is still a (case sensitive!) file. Even a terminal window (/dev/pts/4) or a hard disk (/dev/sdb) is represented somewhere in the file system as a file. It will become clear throughout this course that everything on Linux is a file. 7.3. file The file utility determines the file type. Linux does not use extensions to determine the file type. Your editor does not care whether a file ends in .TXT or .DOC. As a system administrator, you should use the file command to determine the file type. Here are some examples on a typical Linux system. paul@laika:~$ file pic33.png pic33.png: PNG image data, 3840 x 1200, 8-bit/color RGBA, non-interlaced paul@laika:~$ file /etc/passwd /etc/passwd: ASCII text paul@laika:~$ file HelloWorld.c HelloWorld.c: ASCII C program text The file command uses a magic file that contains patterns to recognise file types. The magic file is located in /usr/share/file/magic. Type man 5 magic for more information. It is interesting to point out file -s for special files like those in /dev and /proc. root@debian6~# file /dev/sda /dev/sda: block special root@debian6~# file -s /dev/sda /dev/sda: x86 boot sector; partition 1: ID=0x83, active, starthead... root@debian6~# file /proc/cpuinfo /proc/cpuinfo: empty root@debian6~# file -s /proc/cpuinfo /proc/cpuinfo: ASCII C++ program text 36
  41. 41. working with files 7.4. touch One easy way to create a file is with touch. (We will see many other ways for creating files later in this book.) paul@laika:~/test$ touch paul@laika:~/test$ touch paul@laika:~/test$ touch paul@laika:~/test$ ls -l total 0 -rw-r--r-- 1 paul paul 0 -rw-r--r-- 1 paul paul 0 -rw-r--r-- 1 paul paul 0 file1 file2 file555 2007-01-10 21:40 file1 2007-01-10 21:40 file2 2007-01-10 21:40 file555 touch -t Of course, touch can do more than just create files. Can you determine what by looking at the next screenshot? If not, check the manual for touch. paul@laika:~/test$ touch paul@laika:~/test$ touch paul@laika:~/test$ ls -l total 0 -rw-r--r-- 1 paul paul 0 -rw-r--r-- 1 paul paul 0 -t 200505050000 SinkoDeMayo -t 130207111630 BigBattle 1302-07-11 16:30 BigBattle 2005-05-05 00:00 SinkoDeMayo 7.5. rm When you no longer need a file, use rm to remove it. Unlike some graphical user interfaces, the command line in general does not have a waste bin or trash can to recover files. When you use rm to remove a file, the file is gone. Therefore, be careful when removing files! paul@laika:~/test$ ls BigBattle SinkoDeMayo paul@laika:~/test$ rm BigBattle paul@laika:~/test$ ls SinkoDeMayo rm -i To prevent yourself from accidentally removing a file, you can type rm -i. paul@laika:~/Linux$ touch brel.txt paul@laika:~/Linux$ rm -i brel.txt rm: remove regular empty file `brel.txt'? y paul@laika:~/Linux$ 37
  42. 42. working with files rm -rf By default, rm -r will not remove non-empty directories. However rm accepts several options that will allow you to remove any directory. The rm -rf statement is famous because it will erase anything (providing that you have the permissions to do so). When you are logged on as root, be very careful with rm -rf (the f means force and the r means recursive) since being root implies that permissions don't apply to you. You can literally erase your entire file system by accident. paul@laika:~$ ls test SinkoDeMayo paul@laika:~$ rm test rm: cannot remove `test': Is a directory paul@laika:~$ rm -rf test paul@laika:~$ ls test ls: test: No such file or directory 7.6. cp To copy a file, use cp with a source and a target argument. If the target is a directory, then the source files are copied to that target directory. paul@laika:~/test$ touch FileA paul@laika:~/test$ ls FileA paul@laika:~/test$ cp FileA FileB paul@laika:~/test$ ls FileA FileB paul@laika:~/test$ mkdir MyDir paul@laika:~/test$ ls FileA FileB MyDir paul@laika:~/test$ cp FileA MyDir/ paul@laika:~/test$ ls MyDir/ FileA cp -r To copy complete directories, use cp -r (the -r option forces recursive copying of all files in all subdirectories). paul@laika:~/test$ ls FileA FileB MyDir paul@laika:~/test$ ls MyDir/ FileA paul@laika:~/test$ cp -r MyDir MyDirB paul@laika:~/test$ ls FileA FileB MyDir MyDirB paul@laika:~/test$ ls MyDirB FileA 38
  43. 43. working with files cp multiple files to directory You can also use cp to copy multiple files into a directory. In this case, the last argument (a.k.a. the target) must be a directory. cp file1 file2 dir1/file3 dir1/file55 dir2 cp -i To prevent cp from overwriting existing files, use the -i (for interactive) option. paul@laika:~/test$ cp fire water paul@laika:~/test$ cp -i fire water cp: overwrite `water'? no paul@laika:~/test$ cp -p To preserve permissions and time stamps from source files, use cp -p. paul@laika:~/perms$ cp file* cp paul@laika:~/perms$ cp -p file* cpp paul@laika:~/perms$ ll * -rwx------ 1 paul paul 0 2008-08-25 13:26 file33 -rwxr-x--- 1 paul paul 0 2008-08-25 13:26 file42 cp: total 0 -rwx------ 1 paul paul 0 2008-08-25 13:34 file33 -rwxr-x--- 1 paul paul 0 2008-08-25 13:34 file42 cpp: total 0 -rwx------ 1 paul paul 0 2008-08-25 13:26 file33 -rwxr-x--- 1 paul paul 0 2008-08-25 13:26 file42 7.7. mv Use mv to rename a file or to move the file to another directory. paul@laika:~/test$ paul@laika:~/test$ file100 paul@laika:~/test$ paul@laika:~/test$ ABC.txt paul@laika:~/test$ touch file100 ls mv file100 ABC.txt ls When you need to rename only one file then mv is the preferred command to use. 39
  44. 44. working with files 7.8. rename The rename command can also be used but it has a more complex syntax to enable renaming of many files at once. Below are two examples, the first switches all occurrences of txt to png for all file names ending in .txt. The second example switches all occurrences of upper case ABC in lower case abc for all file names ending in .png . The following syntax will work on debian and ubuntu (prior to Ubuntu 7.10). paul@laika:~/test$ 123.txt ABC.txt paul@laika:~/test$ paul@laika:~/test$ 123.png ABC.png paul@laika:~/test$ paul@laika:~/test$ 123.png abc.png paul@laika:~/test$ ls rename 's/txt/png/' *.txt ls rename 's/ABC/abc/' *.png ls On Red Hat Enterprise Linux (and many other Linux distributions like Ubuntu 8.04), the syntax of rename is a bit different. The first example below renames all *.conf files replacing any occurrence of conf with bak. The second example renames all (*) files replacing one with ONE. [paul@RHEL4a test]$ one.conf two.conf [paul@RHEL4a test]$ [paul@RHEL4a test]$ one.bak two.bak [paul@RHEL4a test]$ [paul@RHEL4a test]$ ONE.bak two.bak [paul@RHEL4a test]$ ls rename conf bak *.conf ls rename one ONE * ls 40
  45. 45. working with files 7.9. practice: working with files 1. List the files in the /bin directory 2. Display the type of file of /bin/cat, /etc/passwd and /usr/bin/passwd. 3a. Download wolf.jpg and LinuxFun.pdf from http://linux-training.be (wget http:// linux-training.be/files/studentfiles/wolf.jpg and wget http://linux-training.be/files/ books/LinuxFun.pdf) 3b. Display the type of file of wolf.jpg and LinuxFun.pdf 3c. Rename wolf.jpg to wolf.pdf (use mv). 3d. Display the type of file of wolf.pdf and LinuxFun.pdf. 4. Create a directory ~/touched and enter it. 5. Create the files today.txt and yesterday.txt in touched. 6. Change the date on yesterday.txt to match yesterday's date. 7. Copy yesterday.txt to copy.yesterday.txt 8. Rename copy.yesterday.txt to kim 9. Create a directory called ~/testbackup and copy all files from ~/touched into it. 10. Use one command to remove the directory ~/testbackup and all files into it. 11. Create a directory ~/etcbackup and copy all *.conf files from /etc into it. Did you include all subdirectories of /etc ? 12. Use rename to rename all *.conf files to *.backup . (if you have more than one distro available, try it on all!) 41
  46. 46. working with files 7.10. solution: working with files 1. List the files in the /bin directory ls /bin 2. Display the type of file of /bin/cat, /etc/passwd and /usr/bin/passwd. file /bin/cat /etc/passwd /usr/bin/passwd 3a. Download wolf.jpg and LinuxFun.pdf from http://linux-training.be (wget http:// linux-training.be/files/studentfiles/wolf.jpg and wget http://linux-training.be/files/ books/LinuxFun.pdf) wget http://linux-training.be/files/studentfiles/wolf.jpg wget http://linux-training.be/files/studentfiles/wolf.png wget http://linux-training.be/files/books/LinuxFun.pdf 3b. Display the type of file of wolf.jpg and LinuxFun.pdf file wolf.jpg LinuxFun.pdf 3c. Rename wolf.jpg to wolf.pdf (use mv). mv wolf.jpg wolf.pdf 3d. Display the type of file of wolf.pdf and LinuxFun.pdf. file wolf.pdf LinuxFun.pdf 4. Create a directory ~/touched and enter it. mkdir ~/touched ; cd ~/touched 5. Create the files today.txt and yesterday.txt in touched. touch today.txt yesterday.txt 6. Change the date on yesterday.txt to match yesterday's date. touch -t 200810251405 yesterday.txt (substitute 20081025 with yesterday) 7. Copy yesterday.txt to copy.yesterday.txt cp yesterday.txt copy.yesterday.txt 8. Rename copy.yesterday.txt to kim mv copy.yesterday.txt kim 9. Create a directory called ~/testbackup and copy all files from ~/touched into it. mkdir ~/testbackup ; cp -r ~/touched ~/testbackup/ 10. Use one command to remove the directory ~/testbackup and all files into it. rm -rf ~/testbackup 11. Create a directory ~/etcbackup and copy all *.conf files from /etc into it. Did you include all subdirectories of /etc ? 42
  47. 47. working with files cp -r /etc/*.conf ~/etcbackup Only *.conf files that are directly in /etc/ are copied. 12. Use rename to rename all *.conf files to *.backup . (if you have more than one distro available, try it on all!) On RHEL: touch 1.conf 2.conf ; rename conf backup *.conf On Debian: touch 1.conf 2.conf ; rename 's/conf/backup/' *.conf 43
  48. 48. Chapter 8. working with file contents Table of Contents 8.1. 8.2. 8.3. 8.4. 8.5. 8.6. 8.7. 8.8. head ................................................................................................................ tail .................................................................................................................. cat ................................................................................................................... tac ................................................................................................................... more and less ................................................................................................. strings ............................................................................................................. practice: file contents ..................................................................................... solution: file contents ..................................................................................... 45 45 46 47 48 48 49 50 In this chapter we will look at the contents of text files with head, tail, cat, tac, more, less and strings. We will also get a glimpse of the possibilities of tools like cat on the command line. 44
  49. 49. working with file contents 8.1. head You can use head to display the first ten lines of a file. paul@laika:~$ head /etc/passwd root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/bin/sh bin:x:2:2:bin:/bin:/bin/sh sys:x:3:3:sys:/dev:/bin/sh sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/bin/sh man:x:6:12:man:/var/cache/man:/bin/sh lp:x:7:7:lp:/var/spool/lpd:/bin/sh mail:x:8:8:mail:/var/mail:/bin/sh news:x:9:9:news:/var/spool/news:/bin/sh paul@laika:~$ The head command can also display the first n lines of a file. paul@laika:~$ head -4 /etc/passwd root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/bin/sh bin:x:2:2:bin:/bin:/bin/sh sys:x:3:3:sys:/dev:/bin/sh Head can also display the first n bytes. paul@laika:~$ head -c4 /etc/passwd rootpaul@laika:~$ 8.2. tail Similar to head, the tail command will display the last ten lines of a file. paul@laika:~$ tail /etc/services vboxd 20012/udp binkp 24554/tcp asp 27374/tcp asp 27374/udp csync2 30865/tcp dircproxy 57000/tcp tfido 60177/tcp fido 60179/tcp # binkp fidonet protocol # Address Search Protocol # # # # cluster synchronization tool Detachable IRC Proxy fidonet EMSI over telnet fidonet EMSI over TCP # Local services paul@laika:~$ You can give tail the number of lines you want to see. $ tail -3 count.txt six seven eight The tail command has other useful options, some of which we will use during this course. 45
  50. 50. working with file contents 8.3. cat The cat command is one of the most universal tools. All it does is copy standard input to standard output. In combination with the shell this can be very powerful and diverse. Some examples will give a glimpse into the possibilities. The first example is simple, you can use cat to display a file on the screen. If the file is longer than the screen, it will scroll to the end. paul@laika:~$ cat /etc/resolv.conf nameserver 194.7.1.4 paul@laika:~$ concatenate cat is short for concatenate. One of the basic uses of cat is to concatenate files into a bigger (or complete) file. paul@laika:~$ paul@laika:~$ paul@laika:~$ paul@laika:~$ one two three paul@laika:~$ echo one > part1 echo two > part2 echo three > part3 cat part1 part2 part3 create files You can use cat to create flat text files. Type the cat > winter.txt command as shown in the screenshot below. Then type one or more lines, finishing each line with the enter key. After the last line, type and hold the Control (Ctrl) key and press d. paul@laika:~/test$ cat > winter.txt It is very cold today! paul@laika:~/test$ cat winter.txt It is very cold today! paul@laika:~/test$ The Ctrl d key combination will send an EOF (End of File) to the running process ending the cat command. 46
  51. 51. working with file contents custom end marker You can choose an end marker for cat with << as is shown in this screenshot. This construction is called a here directive and will end the cat command. paul@laika:~/test$ cat > hot.txt <<stop > It is hot today! > Yes it is summer. > stop paul@laika:~/test$ cat hot.txt It is hot today! Yes it is summer. paul@laika:~/test$ copy files In the third example you will see that cat can be used to copy files. We will explain in detail what happens here in the bash shell chapter. paul@laika:~/test$ cat winter.txt It is very cold today! paul@laika:~/test$ cat winter.txt > cold.txt paul@laika:~/test$ cat cold.txt It is very cold today! paul@laika:~/test$ 8.4. tac Just one example will show you the purpose of tac (as the opposite of cat). paul@laika:~/test$ cat count one two three four paul@laika:~/test$ tac count four three two one paul@laika:~/test$ 47
  52. 52. working with file contents 8.5. more and less The more command is useful for displaying files that take up more than one screen. More will allow you to see the contents of the file page by page. Use the space bar to see the next page, or q to quit. Some people prefer the less command to more. 8.6. strings With the strings command you can display readable ascii strings found in (binary) files. This example locates the ls binary then displays readable strings in the binary file (output is truncated). paul@laika:~$ which ls /bin/ls paul@laika:~$ strings /bin/ls /lib/ld-linux.so.2 librt.so.1 __gmon_start__ _Jv_RegisterClasses clock_gettime libacl.so.1 ... 48
  53. 53. working with file contents 8.7. practice: file contents 1. Display the first 12 lines of /etc/services. 2. Display the last line of /etc/passwd. 3. Use cat to create a file named count.txt that looks like this: One Two Three Four Five 4. Use cp to make a backup of this file to cnt.txt. 5. Use cat to make a backup of this file to catcnt.txt. 6. Display catcnt.txt, but with all lines in reverse order (the last line first). 7. Use more to display /var/log/messages. 8. Display the readable character strings from the /usr/bin/passwd command. 9. Use ls to find the biggest file in /etc. 10. Open two terminal windows (or tabs) and make sure you are in the same directory in both. Type echo this is the first line > tailing.txt in the first terminal, then issue tail -f tailing.txt in the second terminal. Now go back to the first terminal and type echo This is another line >> tailing.txt (note the double >>), verify that the tail -f in the second terminal shows both lines. Stop the tail -f with Ctrl-C. 11. Use cat to create a file named tailing.txt that contains the contents of tailing.txt followed by the contents of /etc/passwd. 12. Use cat to create a file named tailing.txt that contains the contents of tailing.txt preceded by the contents of /etc/passwd. 49
  54. 54. working with file contents 8.8. solution: file contents 1. Display the first 12 lines of /etc/services. head -12 /etc/services 2. Display the last line of /etc/passwd. tail -1 /etc/passwd 3. Use cat to create a file named count.txt that looks like this: cat > count.txt One Two Three Four Five (followed by Ctrl-d) 4. Use cp to make a backup of this file to cnt.txt. cp count.txt cnt.txt 5. Use cat to make a backup of this file to catcnt.txt. cat count.txt > catcnt.txt 6. Display catcnt.txt, but with all lines in reverse order (the last line first). tac catcnt.txt 7. Use more to display /var/log/messages. more /var/log/messages 8. Display the readable character strings from the /usr/bin/passwd command. strings /usr/bin/passwd 9. Use ls to find the biggest file in /etc. ls -lrS /etc 10. Open two terminal windows (or tabs) and make sure you are in the same directory in both. Type echo this is the first line > tailing.txt in the first terminal, then issue tail -f tailing.txt in the second terminal. Now go back to the first terminal and type echo This is another line >> tailing.txt (note the double >>), verify that the tail -f in the second terminal shows both lines. Stop the tail -f with Ctrl-C. 11. Use cat to create a file named tailing.txt that contains the contents of tailing.txt followed by the contents of /etc/passwd. cat /etc/passwd >> tailing.txt 12. Use cat to create a file named tailing.txt that contains the contents of tailing.txt preceded by the contents of /etc/passwd. mv tailing.txt tmp.txt ; cat /etc/passwd tmp.txt > tailing.txt 50
  55. 55. Chapter 9. the Linux file tree Table of Contents 9.1. filesystem hierarchy standard ........................................................................ 52 9.2. man hier ......................................................................................................... 52 9.3. the root directory / ......................................................................................... 52 9.4. binary directories ........................................................................................... 53 9.5. configuration directories ................................................................................ 55 9.6. data directories ............................................................................................... 57 9.7. in memory directories .................................................................................... 59 9.8. /usr Unix System Resources .......................................................................... 64 9.9. /var variable data ............................................................................................ 66 9.10. practice: file system tree .............................................................................. 68 9.11. solution: file system tree .............................................................................. 70 This chapter takes a look at the most common directories in the Linux file tree. It also shows that on Unix everything is a file. 51
  56. 56. the Linux file tree 9.1. filesystem hierarchy standard Many Linux distributions partially follow the Filesystem Hierarchy Standard. The FHS may help make more Unix/Linux file system trees conform better in the future. The FHS is available online at http://www.pathname.com/fhs/ where we read: "The filesystem hierarchy standard has been designed to be used by Unix distribution developers, package developers, and system implementers. However, it is primarily intended to be a reference and is not a tutorial on how to manage a Unix filesystem or directory hierarchy." 9.2. man hier There are some differences in the filesystems between Linux distributions. For help about your machine, enter man hier to find information about the file system hierarchy. This manual will explain the directory structure on your computer. 9.3. the root directory / All Linux systems have a directory structure that starts at the root directory. The root directory is represented by a forward slash, like this: /. Everything that exists on your Linux system can be found below this root directory. Let's take a brief look at the contents of the root directory. [paul@RHELv4u3 ~]$ ls / bin dev home media mnt boot etc lib misc opt proc root 52 sbin selinux srv sys tftpboot tmp usr var
  57. 57. the Linux file tree 9.4. binary directories Binaries are files that contain compiled source code (or machine code). Binaries can be executed on the computer. Sometimes binaries are called executables. /bin The /bin directory contains binaries for use by all users. According to the FHS the / bin directory should contain /bin/cat and /bin/date (among others). In the screenshot below you see common Unix/Linux commands like cat, cp, cpio, date, dd, echo, grep, and so on. Many of these will be covered in this book. paul@laika:~$ ls /bin archdetect egrep autopartition false bash fgconsole bunzip2 fgrep bzcat fuser bzcmp fusermount bzdiff get_mountoptions bzegrep grep bzexe gunzip bzfgrep gzexe bzgrep gzip bzip2 hostname bzip2recover hw-detect bzless ip bzmore kbd_mode cat kill ... mt mt-gnu mv nano nc nc.traditional netcat netstat ntfs-3g ntfs-3g.probe parted_devices parted_server partman partman-commit perform_recipe pidof setupcon sh sh.distrib sleep stralign stty su sync sysfs tailf tar tempfile touch true ulockmgr umount other /bin directories You can find a /bin subdirectory in many other directories. A user named serena could put her own programs in /home/serena/bin. Some applications, often when installed directly from source will put themselves in /opt. A samba server installation can use /opt/samba/bin to store its binaries. /sbin /sbin contains binaries to configure the operating system. Many of the system binaries require root privilege to perform certain tasks. Below a screenshot containing system binaries to change the ip address, partition a disk and create an ext4 file system. paul@ubu1010:~$ ls -l /sbin/ifconfig /sbin/fdisk /sbin/mkfs.ext4 -rwxr-xr-x 1 root root 97172 2011-02-02 09:56 /sbin/fdisk -rwxr-xr-x 1 root root 65708 2010-07-02 09:27 /sbin/ifconfig -rwxr-xr-x 5 root root 55140 2010-08-18 18:01 /sbin/mkfs.ext4 53
  58. 58. the Linux file tree /lib Binaries found in /bin and /sbin often use shared libraries located in /lib. Below is a screenshot of the partial contents of /lib. paul@laika:~$ ls /lib/libc* /lib/libc-2.5.so /lib/libcfont.so.0.0.0 /lib/libcap.so.1 /lib/libcidn-2.5.so /lib/libcap.so.1.10 /lib/libcidn.so.1 /lib/libcfont.so.0 /lib/libcom_err.so.2 /lib/libcom_err.so.2.1 /lib/libconsole.so.0 /lib/libconsole.so.0.0.0 /lib/libcrypt-2.5.so /lib/modules Typically, the Linux kernel loads kernel modules from /lib/modules/$kernelversion/. This directory is discussed in detail in the Linux kernel chapter. /lib32 and /lib64 We currently are in a transition between 32-bit and 64-bit systems. Therefore, you may encounter directories named /lib32 and /lib64 which clarify the register size used during compilation time of the libraries. A 64-bit computer may have some 32-bit binaries and libraries for compatibility with legacy applications. This screenshot uses the file utility to demonstrate the difference. paul@laika:~$ file /lib32/libc-2.5.so /lib32/libc-2.5.so: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), for GNU/Linux 2.6.0, stripped paul@laika:~$ file /lib64/libcap.so.1.10 /lib64/libcap.so.1.10: ELF 64-bit LSB shared object, AMD x86-64, version 1 (SYSV), stripped The ELF (Executable and Linkable Format) is used in almost every Unix-like operating system since System V. /opt The purpose of /opt is to store optional software. In many cases this is software from outside the distribution repository. You may find an empty /opt directory on many systems. A large package can install all its files in /bin, /lib, /etc subdirectories within /opt/ $packagename/. If for example the package is called wp, then it installs in /opt/wp, putting binaries in /opt/wp/bin and manpages in /opt/wp/man. 54
  59. 59. the Linux file tree 9.5. configuration directories /boot The /boot directory contains all files needed to boot the computer. These files don't change very often. On Linux systems you typically find the /boot/grub directory here. /boot/grub contains /boot/grub/grub.cfg (older systems may still have /boot/ grub/grub.conf) which defines the boot menu that is displayed before the kernel starts. /etc All of the machine-specific configuration files should be located in /etc. Historically /etc stood for etcetera, today people often use the Editable Text Configuration backronym. Many times the name of a configuration files is the same as the application, daemon, or protocol with .conf added as the extension. paul@laika:~$ ls /etc/*.conf /etc/adduser.conf /etc/ld.so.conf /etc/brltty.conf /etc/lftp.conf /etc/ccertificates.conf /etc/libao.conf /etc/cvs-cron.conf /etc/logrotate.conf /etc/ddclient.conf /etc/ltrace.conf /etc/debconf.conf /etc/mke2fs.conf /etc/deluser.conf /etc/netscsid.conf /etc/fdmount.conf /etc/nsswitch.conf /etc/hdparm.conf /etc/pam.conf /etc/host.conf /etc/pnm2ppa.conf /etc/inetd.conf /etc/povray.conf /etc/kernel-img.conf /etc/resolv.conf paul@laika:~$ /etc/scrollkeeper.conf /etc/sysctl.conf /etc/syslog.conf /etc/ucf.conf /etc/uniconf.conf /etc/updatedb.conf /etc/usplash.conf /etc/uswsusp.conf /etc/vnc.conf /etc/wodim.conf /etc/wvdial.conf There is much more to be found in /etc. /etc/init.d/ A lot of Unix/Linux distributions have an /etc/init.d directory that contains scripts to start and stop daemons. This directory could disappear as Linux migrates to systems that replace the old init way of starting all daemons. /etc/X11/ The graphical display (aka X Window System or just X) is driven by software from the X.org foundation. The configuration file for your graphical display is /etc/X11/ xorg.conf. 55
  60. 60. the Linux file tree /etc/skel/ The skeleton directory /etc/skel is copied to the home directory of a newly created user. It usually contains hidden files like a .bashrc script. /etc/sysconfig/ This directory, which is not mentioned in the FHS, contains a lot of Red Hat Enterprise Linux configuration files. We will discuss some of them in greater detail. The screenshot below is the /etc/sysconfig directory from RHELv4u4 with everything installed. paul@RHELv4u4:~$ ls /etc/sysconfig/ apmd firstboot irda apm-scripts grub irqbalance authconfig hidd keyboard autofs httpd kudzu bluetooth hwconf lm_sensors clock i18n mouse console init mouse.B crond installinfo named desktop ipmi netdump diskdump iptables netdump_id_dsa dund iptables-cfg netdump_id_dsa.p paul@RHELv4u4:~$ network networking ntpd openib.conf pand pcmcia pgsql prelink rawdevices rhn samba saslauthd selinux spamassassin squid syslog sys-config-sec sys-config-users sys-logviewer tux vncservers xinetd The file /etc/sysconfig/firstboot tells the Red Hat Setup Agent not to run at boot time. If you want to run the Red Hat Setup Agent at the next reboot, then simply remove this file, and run chkconfig --level 5 firstboot on. The Red Hat Setup Agent allows you to install the latest updates, create a user account, join the Red Hat Network and more. It will then create the /etc/sysconfig/firstboot file again. paul@RHELv4u4:~$ cat /etc/sysconfig/firstboot RUN_FIRSTBOOT=NO The /etc/sysconfig/harddisks file contains some parameters to tune the hard disks. The file explains itself. You can see hardware detected by kudzu in /etc/sysconfig/hwconf. Kudzu is software from Red Hat for automatic discovery and configuration of hardware. The keyboard type and keymap table are set in the /etc/sysconfig/keyboard file. For more console keyboard information, check the manual pages of keymaps(5), dumpkeys(1), loadkeys(1) and the directory /lib/kbd/keymaps/. root@RHELv4u4:/etc/sysconfig# cat keyboard KEYBOARDTYPE="pc" KEYTABLE="us" We will discuss networking files in this directory in the networking chapter. 56
  61. 61. the Linux file tree 9.6. data directories /home Users can store personal or project data under /home. It is common (but not mandatory by the fhs) practice to name the users home directory after the user name in the format /home/$USERNAME. For example: paul@ubu606:~$ ls /home geert annik sandra paul tom Besides giving every user (or every project or group) a location to store personal files, the home directory of a user also serves as a location to store the user profile. A typical Unix user profile contains many hidden files (files whose file name starts with a dot). The hidden files of the Unix user profiles contain settings specific for that user. paul@ubu606:~$ ls -d /home/paul/.* /home/paul/. /home/paul/.bash_profile /home/paul/.. /home/paul/.bashrc /home/paul/.bash_history /home/paul/.lesshst /home/paul/.ssh /home/paul/.viminfo /root On many systems /root is the default location for personal data and profile of the root user. If it does not exist by default, then some administrators create it. /srv You may use /srv for data that is served by your system. The FHS allows locating cvs, rsync, ftp and www data in this location. The FHS also approves administrative naming in /srv, like /srv/project55/ftp and /srv/sales/www. On Sun Solaris (or Oracle Solaris) /export is used for this purpose. /media The /media directory serves as a mount point for removable media devices such as CD-ROM's, digital cameras, and various usb-attached devices. Since /media is rather new in the Unix world, you could very well encounter systems running without this directory. Solaris 9 does not have it, Solaris 10 does. Most Linux distributions today mount all removable media in /media. paul@debian5:~$ ls /media/ cdrom cdrom0 usbdisk 57
  62. 62. the Linux file tree /mnt The /mnt directory should be empty and should only be used for temporary mount points (according to the FHS). Unix and Linux administrators used to create many directories here, like /mnt/ something/. You likely will encounter many systems with more than one directory created and/or mounted inside /mnt to be used for various local and remote filesystems. /tmp Applications and users should use /tmp to store temporary data when needed. Data stored in /tmp may use either disk space or RAM. Both of which are managed by the operating system. Never use /tmp to store data that is important or which you wish to archive. 58
  63. 63. the Linux file tree 9.7. in memory directories /dev Device files in /dev appear to be ordinary files, but are not actually located on the hard disk. The /dev directory is populated with files as the kernel is recognising hardware. common physical devices Common hardware such as hard disk devices are represented by device files in /dev. Below a screenshot of SATA device files on a laptop and then IDE attached drives on a desktop. (The detailed meaning of these devices will be discussed later.) # # SATA or SCSI or USB # paul@laika:~$ ls /dev/sd* /dev/sda /dev/sda1 /dev/sda2 /dev/sda3 /dev/sdb /dev/sdb1 /dev/sdb2 # # IDE or ATAPI # paul@barry:~$ ls /dev/hd* /dev/hda /dev/hda1 /dev/hda2 /dev/hdb /dev/hdb1 /dev/hdb2 /dev/hdc Besides representing physical hardware, some device files are special. These special devices can be very useful. /dev/tty and /dev/pts For example, /dev/tty1 represents a terminal or console attached to the system. (Don't break your head on the exact terminology of 'terminal' or 'console', what we mean here is a command line interface.) When typing commands in a terminal that is part of a graphical interface like Gnome or KDE, then your terminal will be represented as /dev/pts/1 (1 can be another number). /dev/null On Linux you will find other special devices such as /dev/null which can be considered a black hole; it has unlimited storage, but nothing can be retrieved from it. Technically speaking, anything written to /dev/null will be discarded. /dev/null can be useful to discard unwanted output from commands. /dev/null is not a good location to store your backups ;-). 59
  64. 64. the Linux file tree /proc conversation with the kernel /proc is another special directory, appearing to be ordinary files, but not taking up disk space. It is actually a view of the kernel, or better, what the kernel manages, and is a means to interact with it directly. /proc is a proc filesystem. paul@RHELv4u4:~$ mount -t proc none on /proc type proc (rw) When listing the /proc directory you will see many numbers (on any Unix) and some interesting files (on Linux) mul@laika:~$ ls /proc 1 2339 4724 5418 10175 2523 4729 5421 10211 2783 4741 5658 10239 2975 4873 5661 141 29775 4874 5665 15045 29792 4878 5927 1519 2997 4879 6 1548 3 4881 6032 1551 30228 4882 6033 1554 3069 5 6145 1557 31422 5073 6298 1606 3149 5147 6414 180 31507 5203 6418 181 3189 5206 6419 182 3193 5228 6420 18898 3246 5272 6421 19799 3248 5291 6422 19803 3253 5294 6423 19804 3372 5356 6424 1987 4 5370 6425 1989 42 5379 6426 2 45 5380 6430 20845 4542 5412 6450 221 46 5414 6551 2338 4704 5416 6568 6587 6596 6599 6638 6652 6719 6736 6737 6755 6762 6774 6816 6991 6993 6996 7157 7163 7164 7171 7175 7188 7189 7191 7192 7199 7201 7204 7206 7214 7216 7218 7223 7224 7227 7260 7267 7275 7282 7298 7319 7330 7345 7513 7525 7529 9964 acpi asound buddyinfo bus cmdline cpuinfo crypto devices diskstats dma driver execdomains fb filesystems fs ide interrupts iomem ioports irq kallsyms kcore key-users kmsg loadavg locks meminfo misc modules mounts mtrr net pagetypeinfo partitions sched_debug scsi self slabinfo stat swaps sys sysrq-trigger sysvipc timer_list timer_stats tty uptime version version_signature vmcore vmnet vmstat zoneinfo Let's investigate the file properties inside /proc. Looking at the date and time will display the current date and time showing the files are constantly updated (a view on the kernel). paul@RHELv4u4:~$ date Mon Jan 29 18:06:32 EST 2007 paul@RHELv4u4:~$ ls -al /proc/cpuinfo -r--r--r-- 1 root root 0 Jan 29 18:06 /proc/cpuinfo paul@RHELv4u4:~$ paul@RHELv4u4:~$ ...time passes... paul@RHELv4u4:~$ paul@RHELv4u4:~$ date Mon Jan 29 18:10:00 EST 2007 paul@RHELv4u4:~$ ls -al /proc/cpuinfo -r--r--r-- 1 root root 0 Jan 29 18:10 /proc/cpuinfo 60
  65. 65. the Linux file tree Most files in /proc are 0 bytes, yet they contain data--sometimes a lot of data. You can see this by executing cat on files like /proc/cpuinfo, which contains information about the CPU. paul@RHELv4u4:~$ file /proc/cpuinfo /proc/cpuinfo: empty paul@RHELv4u4:~$ cat /proc/cpuinfo processor : 0 vendor_id : AuthenticAMD cpu family : 15 model : 43 model name : AMD Athlon(tm) 64 X2 Dual Core Processor 4600+ stepping : 1 cpu MHz : 2398.628 cache size : 512 KB fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 1 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge... bogomips : 4803.54 Just for fun, here is /proc/cpuinfo on a Sun Sunblade 1000... paul@pasha:~$ cat /proc/cpuinfo cpu : TI UltraSparc III (Cheetah) fpu : UltraSparc III integrated FPU promlib : Version 3 Revision 2 prom : 4.2.2 type : sun4u ncpus probed : 2 ncpus active : 2 Cpu0Bogo : 498.68 Cpu0ClkTck : 000000002cb41780 Cpu1Bogo : 498.68 Cpu1ClkTck : 000000002cb41780 MMU Type : Cheetah State: CPU0: online CPU1: online Most of the files in /proc are read only, some require root privileges, some files are writable, and many files in /proc/sys are writable. Let's discuss some of the files in / proc. 61
  66. 66. the Linux file tree /proc/interrupts On the x86 architecture, /proc/interrupts displays the interrupts. paul@RHELv4u4:~$ cat /proc/interrupts CPU0 0: 13876877 IO-APIC-edge timer 1: 15 IO-APIC-edge i8042 8: 1 IO-APIC-edge rtc 9: 0 IO-APIC-level acpi 12: 67 IO-APIC-edge i8042 14: 128 IO-APIC-edge ide0 15: 124320 IO-APIC-edge ide1 169: 111993 IO-APIC-level ioc0 177: 2428 IO-APIC-level eth0 NMI: 0 LOC: 13878037 ERR: 0 MIS: 0 On a machine with two CPU's, the file looks like this. paul@laika:~$ cat /proc/interrupts CPU0 CPU1 0: 860013 0 IO-APIC-edge 1: 4533 0 IO-APIC-edge 7: 0 0 IO-APIC-edge 8: 6588227 0 IO-APIC-edge 10: 2314 0 IO-APIC-fasteoi 12: 133 0 IO-APIC-edge 14: 0 0 IO-APIC-edge 15: 72269 0 IO-APIC-edge 18: 1 0 IO-APIC-fasteoi 19: 115036 0 IO-APIC-fasteoi 20: 126871 0 IO-APIC-fasteoi 21: 30204 0 IO-APIC-fasteoi 22: 1334 0 IO-APIC-fasteoi 24: 234739 0 IO-APIC-fasteoi NMI: 72 42 LOC: 860000 859994 ERR: 0 timer i8042 parport0 rtc acpi i8042 libata libata yenta eth0 libata, ohci1394 ehci_hcd:usb1, uhci_hcd:usb2 saa7133[0], saa7133[0] nvidia /proc/kcore The physical memory is represented in /proc/kcore. Do not try to cat this file, instead use a debugger. The size of /proc/kcore is the same as your physical memory, plus four bytes. paul@laika:~$ ls -lh /proc/kcore -r-------- 1 root root 2.0G 2007-01-30 08:57 /proc/kcore paul@laika:~$ 62
  67. 67. the Linux file tree /sys Linux 2.6 hot plugging The /sys directory was created for the Linux 2.6 kernel. Since 2.6, Linux uses sysfs to support usb and IEEE 1394 (FireWire) hot plug devices. See the manual pages of udev(8) (the successor of devfs) and hotplug(8) for more info (or visit http://linuxhotplug.sourceforge.net/ ). Basically the /sys directory contains kernel information about hardware. 63
  68. 68. the Linux file tree 9.8. /usr Unix System Resources Although /usr is pronounced like user, remember that it stands for Unix System Resources. The /usr hierarchy should contain shareable, read only data. Some people choose to mount /usr as read only. This can be done from its own partition or from a read only NFS share. /usr/bin The /usr/bin directory contains a lot of commands. paul@deb508:~$ ls /usr/bin | wc -l 1395 (On Solaris the /bin directory is a symbolic link to /usr/bin.) /usr/include The /usr/include directory contains general use include files for C. paul@ubu1010:~$ ls /usr/include/ aalib.h expat_config.h af_vfs.h expat_external.h aio.h expat.h AL fcntl.h aliases.h features.h ... math.h mcheck.h memory.h menu.h mntent.h search.h semaphore.h setjmp.h sgtty.h shadow.h /usr/lib The /usr/lib directory contains libraries that are not directly executed by users or scripts. paul@deb508:~$ ls /usr/lib | head -7 4Suite ao apt arj aspell avahi bonobo /usr/local The /usr/local directory can be used by an administrator to install software locally. paul@deb508:~$ ls /usr/local/ bin etc games include lib man paul@deb508:~$ du -sh /usr/local/ 128K /usr/local/ 64 sbin share src
  69. 69. the Linux file tree /usr/share The /usr/share directory contains architecture independent data. As you can see, this is a fairly large directory. paul@deb508:~$ ls /usr/share/ | wc -l 263 paul@deb508:~$ du -sh /usr/share/ 1.3G /usr/share/ This directory typically contains /usr/share/man for manual pages. paul@deb508:~$ ls /usr/share/man cs fr hu it.UTF-8 man2 man6 pl.ISO8859-2 sv de fr.ISO8859-1 id ja man3 man7 pl.UTF-8 tr es fr.UTF-8 it ko man4 man8 pt_BR zh_CN fi gl it.ISO8859-1 man1 man5 pl ru zh_TW And it contains /usr/share/games for all static game data (so no high-scores or play logs). paul@ubu1010:~$ ls /usr/share/games/ openttd wesnoth /usr/src The /usr/src directory is the recommended location for kernel source files. paul@deb508:~$ ls -l /usr/src/ total 12 drwxr-xr-x 4 root root 4096 2011-02-01 14:43 linux-headers-2.6.26-2-686 drwxr-xr-x 18 root root 4096 2011-02-01 14:43 linux-headers-2.6.26-2-common drwxr-xr-x 3 root root 4096 2009-10-28 16:01 linux-kbuild-2.6.26 65
  70. 70. the Linux file tree 9.9. /var variable data Files that are unpredictable in size, such as log, cache and spool files, should be located in /var. /var/log The /var/log directory serves as a central point to contain all log files. [paul@RHEL4b ~]$ ls /var/log acpid cron.2 maillog.2 amanda cron.3 maillog.3 anaconda.log cron.4 maillog.4 anaconda.syslog cups mailman anaconda.xlog dmesg messages audit exim messages.1 boot.log gdm messages.2 boot.log.1 httpd messages.3 boot.log.2 iiim messages.4 boot.log.3 iptraf mysqld.log boot.log.4 lastlog news canna mail pgsql cron maillog ppp cron.1 maillog.1 prelink.log quagga radius rpmpkgs rpmpkgs.1 rpmpkgs.2 rpmpkgs.3 rpmpkgs.4 sa samba scrollkeeper.log secure secure.1 secure.2 secure.3 secure.4 spooler spooler.1 spooler.2 spooler.3 spooler.4 squid uucp vbox vmware-tools-guestd wtmp wtmp.1 Xorg.0.log Xorg.0.log.old /var/log/messages A typical first file to check when troubleshooting on Red Hat (and derivatives) is the /var/log/messages file. By default this file will contain information on what just happened to the system. The file is called /var/log/syslog on Debian and Ubuntu. [root@RHEL4b ~]# tail /var/log/messages Jul 30 05:13:56 anacron: anacron startup succeeded Jul 30 05:13:56 atd: atd startup succeeded Jul 30 05:13:57 messagebus: messagebus startup succeeded Jul 30 05:13:57 cups-config-daemon: cups-config-daemon startup succeeded Jul 30 05:13:58 haldaemon: haldaemon startup succeeded Jul 30 05:14:00 fstab-sync[3560]: removed all generated mount points Jul 30 05:14:01 fstab-sync[3628]: added mount point /media/cdrom for... Jul 30 05:14:01 fstab-sync[3646]: added mount point /media/floppy for... Jul 30 05:16:46 sshd(pam_unix)[3662]: session opened for user paul by... Jul 30 06:06:37 su(pam_unix)[3904]: session opened for user root by paul /var/cache The /var/cache directory can contain cache data for several applications. paul@ubu1010:~$ ls /var/cache/ apt dictionaries-common binfmts flashplugin-installer cups fontconfig debconf fonts gdm hald jockey ldconfig 66 man pm-utils pppconfig samba software-center
  71. 71. the Linux file tree /var/spool The /var/spool directory typically contains spool directories for mail and cron, but also serves as a parent directory for other spool files (for example print spool files). /var/lib The /var/lib directory contains application state information. Red Hat Enterprise Linux for example keeps files pertaining to rpm in /var/lib/rpm/. /var/... /var also contains Process ID files in /var/run (soon to be replaced with /run) and temporary files that survive a reboot in /var/tmp and information about file locks in /var/lock. There will be more examples of /var usage further in this book. 67
  72. 72. the Linux file tree 9.10. practice: file system tree 1. Does the file /bin/cat exist ? What about /bin/dd and /bin/echo. What is the type of these files ? 2. What is the size of the Linux kernel file(s) (vmlinu*) in /boot ? 3. Create a directory ~/test. Then issue the following commands: cd ~/test dd if=/dev/zero of=zeroes.txt count=1 bs=100 od zeroes.txt dd will copy one times (count=1) a block of size 100 bytes (bs=100) from the file / dev/zero to ~/test/zeroes.txt. Can you describe the functionality of /dev/zero ? 4. Now issue the following command: dd if=/dev/random of=random.txt count=1 bs=100 ; od random.txt dd will copy one times (count=1) a block of size 100 bytes (bs=100) from the file / dev/random to ~/test/random.txt. Can you describe the functionality of /dev/random ? 5. Issue the following two commands, and look at the first character of each output line. ls -l /dev/sd* /dev/hd* ls -l /dev/tty* /dev/input/mou* The first ls will show block(b) devices, the second ls shows character(c) devices. Can you tell the difference between block and character devices ? 6. Use cat to display /etc/hosts and /etc/resolv.conf. What is your idea about the purpose of these files ? 7. Are there any files in /etc/skel/ ? Check also for hidden files. 8. Display /proc/cpuinfo. On what architecture is your Linux running ? 9. Display /proc/interrupts. What is the size of this file ? Where is this file stored ? 10. Can you enter the /root directory ? Are there (hidden) files ? 11. Are ifconfig, fdisk, parted, shutdown and grub-install present in /sbin ? Why are these binaries in /sbin and not in /bin ? 12. Is /var/log a file or a directory ? What about /var/spool ? 13. Open two command prompts (Ctrl-Shift-T in gnome-terminal) or terminals (CtrlAlt-F1, Ctrl-Alt-F2, ...) and issue the who am i in both. Then try to echo a word from one terminal to the other. 68
  73. 73. the Linux file tree 14. Read the man page of random and explain the difference between /dev/random and /dev/urandom. 69
  74. 74. the Linux file tree 9.11. solution: file system tree 1. Does the file /bin/cat exist ? What about /bin/dd and /bin/echo. What is the type of these files ? ls /bin/cat ; file /bin/cat ls /bin/dd ; file /bin/dd ls /bin/echo ; file /bin/echo 2. What is the size of the Linux kernel file(s) (vmlinu*) in /boot ? ls -lh /boot/vm* 3. Create a directory ~/test. Then issue the following commands: cd ~/test dd if=/dev/zero of=zeroes.txt count=1 bs=100 od zeroes.txt dd will copy one times (count=1) a block of size 100 bytes (bs=100) from the file / dev/zero to ~/test/zeroes.txt. Can you describe the functionality of /dev/zero ? /dev/zero is a Linux special device. It can be considered a source of zeroes. You cannot send something to /dev/zero, but you can read zeroes from it. 4. Now issue the following command: dd if=/dev/random of=random.txt count=1 bs=100 ; od random.txt dd will copy one times (count=1) a block of size 100 bytes (bs=100) from the file / dev/random to ~/test/random.txt. Can you describe the functionality of /dev/random ? /dev/random acts as a random number generator on your Linux machine. 5. Issue the following two commands, and look at the first character of each output line. ls -l /dev/sd* /dev/hd* ls -l /dev/tty* /dev/input/mou* The first ls will show block(b) devices, the second ls shows character(c) devices. Can you tell the difference between block and character devices ? Block devices are always written to (or read from) in blocks. For hard disks, blocks of 512 bytes are common. Character devices act as a stream of characters (or bytes). Mouse and keyboard are typical character devices. 6. Use cat to display /etc/hosts and /etc/resolv.conf. What is your idea about the purpose of these files ? 70
  75. 75. the Linux file tree /etc/hosts contains hostnames with their ip address /etc/resolv.conf should contain the ip address of a DNS name server. 7. Are there any files in /etc/skel/ ? Check also for hidden files. Issue "ls -al /etc/skel/". Yes, there should be hidden files there. 8. Display /proc/cpuinfo. On what architecture is your Linux running ? The file should contain at least one line with Intel or other cpu. 9. Display /proc/interrupts. What is the size of this file ? Where is this file stored ? The size is zero, yet the file contains data. It is not stored anywhere because /proc is a virtual file system that allows you to talk with the kernel. (If you answered "stored in RAM-memory, that is also correct...). 10. Can you enter the /root directory ? Are there (hidden) files ? Try "cd /root". Yes there are (hidden) files there. 11. Are ifconfig, fdisk, parted, shutdown and grub-install present in /sbin ? Why are these binaries in /sbin and not in /bin ? Because those files are only meant for system administrators. 12. Is /var/log a file or a directory ? What about /var/spool ? Both are directories. 13. Open two command prompts (Ctrl-Shift-T in gnome-terminal) or terminals (CtrlAlt-F1, Ctrl-Alt-F2, ...) and issue the who am i in both. Then try to echo a word from one terminal to the other. tty-terminal: echo Hello > /dev/tty1 pts-terminal: echo Hello > /dev/pts/1 14. Read the man page of random and explain the difference between /dev/random and /dev/urandom. man 4 random 71
  76. 76. Part III. shell expansion
  77. 77. Chapter 10. commands and arguments Table of Contents 10.1. 10.2. 10.3. 10.4. 10.5. 10.6. 10.7. echo .............................................................................................................. arguments ..................................................................................................... commands .................................................................................................... aliases ........................................................................................................... displaying shell expansion ........................................................................... practice: commands and arguments ............................................................. solution: commands and arguments ............................................................. 74 74 76 77 78 79 81 This chapter introduces you to shell expansion by taking a close look at commands and arguments. Knowing shell expansion is important because many commands on your Linux system are processed and most likely changed by the shell before they are executed. The command line interface or shell used on most Linux systems is called bash, which stands for Bourne again shell. The bash shell incorporates features from sh (the original Bourne shell), csh (the C shell), and ksh (the Korn shell). 73
  78. 78. commands and arguments 10.1. echo This chapter frequently uses the echo command to demonstrate shell features. The echo command is very simple: it echoes the input that it receives. paul@laika:~$ echo Burtonville Burtonville paul@laika:~$ echo Smurfs are blue Smurfs are blue 10.2. arguments One of the primary features of a shell is to perform a command line scan. When you enter a command at the shell's command prompt and press the enter key, then the shell will start scanning that line, cutting it up in arguments. While scanning the line, the shell may make many changes to the arguments you typed. This process is called shell expansion. When the shell has finished scanning and modifying that line, then it will be executed. white space removal Parts that are separated by one or more consecutive white spaces (or tabs) are considered separate arguments, any white space is removed. The first argument is the command to be executed, the other arguments are given to the command. The shell effectively cuts your command into one or more arguments. This explains why the following four different command lines are the same after shell expansion. [paul@RHELv4u3 Hello World [paul@RHELv4u3 Hello World [paul@RHELv4u3 Hello World [paul@RHELv4u3 Hello World ~]$ echo Hello World ~]$ echo Hello ~]$ echo ~]$ World echo Hello World Hello World The echo command will display each argument it receives from the shell. The echo command will also add a new white space between the arguments it received. single quotes You can prevent the removal of white spaces by quoting the spaces. The contents of the quoted string are considered as one argument. In the screenshot below the echo receives only one argument. [paul@RHEL4b ~]$ echo 'A line with A line with single quotes [paul@RHEL4b ~]$ 74 single quotes'
  79. 79. commands and arguments double quotes You can also prevent the removal of white spaces by double quoting the spaces. Same as above, echo only receives one argument. [paul@RHEL4b ~]$ echo "A line with A line with double quotes [paul@RHEL4b ~]$ double quotes" Later in this book, when discussing variables we will see important differences between single and double quotes. echo and quotes Quoted lines can include special escaped characters recognised by the echo command (when using echo -e). The screenshot below shows how to use n for a newline and t for a tab (usually eight white spaces). [paul@RHEL4b A line with a newline [paul@RHEL4b A line with a newline [paul@RHEL4b A line with [paul@RHEL4b A line with [paul@RHEL4b ~]$ echo -e "A line with na newline" ~]$ echo -e 'A line with na newline' ~]$ echo -e "A line with ta tab" a tab ~]$ echo -e 'A line with ta tab' a tab ~]$ The echo command can generate more than white spaces, tabs and newlines. Look in the man page for a list of options. 75

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